1. Field of the Invention
The present invention relates to new alkaline earth metal fluosilicates which are activated with divalent europium and are useful as luminescent materials.
2. Description of the Prior Art
Divalent europium is a well known activator for luminescent materials and it usually produces broad band emissions in the visible blue region and the near ultraviolet region. Compounds which are activated with divalent europium and which exhibit a narrow band emission in the near ultraviolet region are also known. Thus, the U.S. Pat. No. 3,630,945 discloses alkaline earth metal aluminum fluorides which are activated with divalent europium and which exhibit a sharp line ultraviolet emission spectrum which is characterized by 4f to 4f energy level transitions. Nevertheless, this spectrum exhibits the disadvantage of a broadening of the base of the emission peak which results from an emission which is due to 5f to 4f transitions. This proves to be troublesome for any applications which require a spectral separation of a very narrow emission.